1. Field of the Invention
The present invention relates to an electric starter motor having an intermediate gear that constantly intermeshes with a pinion, the electric starter motor transmitting torque imparted by an output shaft of an electric motor from the pinion through the intermediate gear to a ring gear.
2. Description of the Related Art
Conventional electric starter motors include: an output shaft for imparting torque; a pinion disposed on the output shaft so as to be movable axially, rotation of the output shaft being transmitted to rotate the pinion; an intermediate shaft disposed parallel to the output shaft; an intermediate gear intermeshing with the pinion, the intermediate gear being rotatably supported by the intermediate shaft, and also being disposed on the intermediate shaft so as to be movable axially; and an anchoring member engaging with a pinion boss portion disposed on the pinion and a cylindrical boss portion disposed on the intermediate gear so as to be rotatable relative to each other, the anchoring member restricting relative axial movement between the pinion and the intermediate gear. When starting an internal combustion engine, the intermediate gear is moved axially with the pinion by means of the anchoring member so as to be engaged with a ring gear of the internal combustion engine. Thus, torque imparted by the output shaft is transmitted from the pinion through the intermediate gear to the ring gear to start the engine. (See Patent Literature 1, for example.)
Patent Literature 1: Japanese Patent Laid-Open No. 2002-180937 (Gazette)
In conventional electric starter motors, the anchoring member (corresponding to the movement linking body of the present invention) is positioned between a pinion flange portion and a clutch cover, and restricts axial movement of the pinion. Since it is necessary to permit relative rotation of the pinion and the intermediate gear, it is necessary to make the thickness of the anchoring member slightly smaller than a dimension between the pinion flange portion and the clutch cover. Specifically, it is necessary to dispose some clearance between the anchoring member and the clutch cover when the anchoring member is in contact with the pinion flange portion.
Now, the clutch cover is mounted so as to be fitted over a clutch outer with a washer interposed. Thus, in addition to dimensional precision of the pinion, the dimension between the pinion flange portion and the clutch cover is affected by sheet thickness of the washer and the clutch cover, and also by flatness of the washer and the clutch cover. In addition, there may also be irregularities in the thickness of the anchoring member. From these points, it is necessary to predesign the dimension between the pinion flange portion and the clutch cover so as to have a comparatively large dimension.
Since the pinion and the clutch cover and the anchoring member rotate relative to each other while the electric starter motor is operating, the sliding surfaces of the anchoring member relative to the pinion flange portion and the clutch cover are abraded with repeated use, further increasing the clearance between the anchoring member and the clutch cover. Thus, the intermediate gear may have too much play.